im comparing a 850i year 1990 to a m3 from year 1994, and there is still a horsepower difference, and the 850 is even more expensive. you do your math.
BMW was NEVER about straightout horsepower. Besides you are comparing an M car engine to a luxury/crusier V12. To be fair why don't you compare the S54 motor (E46 M3) to the V12 in the Mcclaren F1, which, is a BMW motor with over 600hp, but that's not fair as well as both are completely different motors with completely different purposes.
If you want horsepower consider Mercedes AMG, or a flat out sports car like 911 turbo, viper, or vette. BMW is about sharp handling, comfort, and overall sporty feel with emphasis on "precise steering feel."